The technical sector of the invention is that of the construction of automatic machines or robots for writing various graphics on diverse supports.
One application of the processes and devices according to the invention is the mass-production of flat panels bearing legends and/or drawings or graphics, for example advertizing boards, displays, indicator panels, decorative or advertizing patterns on various supports, packings, etc. . . .
The processes and devices according to the invention also make it possible automatically to write graphics on supports having a surface with a slight curvature, for example on car bodies, curved panels, various industrial products, on curved walls.
The coloured liquids which may be used on the devices according to the invention may be paints, inks or any other liquid vehicle containing a colorant.
The robots according to the invention make it possible to write letters, figures or polychrome graphics which are made by projecting drops of coloured liquid which produce very small coloured dots, very close to one another, with the result that a very good resolution is obtained and the eye cannot perceive any discontinuity in the graphics.
The production of so-called high-resolution or high-quality graphics requires very numerous operations and very numerous controls, since the number of dots is very high.
Such controls are compulsory not only to check the parameters influencing the circulation of the coloured liquids, but also to check that the different films of the support or supports have been correctly produced.
Controls during execution of the graphics by automatic devices which project drops of liquid, must be precise and rapid in order to avoid the automatic device being blocked due to poor projection of the liquids and in order to check that the film or films have been correctly produced. The displacements of the tools for projecting the coloured liquids and the results obtained must be able to be checked at any instant.
It is recalled that the supports of diverse composition adapted to bear high-resolution graphics must comprise one or more sub-layers called films. These sub-layers ensure protection of the support and the quality of the graphics.
Various processes for writing graphics on various supports are known.
One of the most used techniques is the technique of printing books or newspapers in printing houses equipped with rotary presses which are very large machines. This technique is reserved for printing on paper or on sheets and for very large numbers of copies.
Computer printers used for writing data or simple graphics on strips of paper, are known. In particular, ink jet computer printers exist, which comprise an ink projecting nozzle equipped with a piezoelectric ceramic element which divides the jet of ink into drops.
In the known ink jet printers, printing is effected on a support, for example on a strip of paper, which advances in front of the ink projecting nozzle and the latter comprises means for electrically charging the drops of ink then for deviating them electrically in a direction perpendicular to the direction of displacement of the support to be printed.
Plotting tables are also known, associated with a computer which controls relative displacements of a plotting stylus and of the table along two axes perpendicular to each other and parallel to the plane of the table.
Painting robots are also known which comprise a gun supported by an articulated arm which makes it possible to apply coats of paint on a support.
The proceses and devices according to the invention combine in novel manner part of the techniques of projection of drops of liquid used in ink jet printers and part of the techniques used in plotting tables to obtain a relative displacement of the support with respect to the writing tool.
FR-A-2 601 265 (CHERUBIN-GRILLO) describes a device for printing, dot by dot, a polychrome image on a fixed support which comprises a projecting head, adapted to be displaced along three rectangular axes, which bears a plurality of nozzles whose axes converge at a point close to the support. Each nozzle projects a liquid of a determined colour and the colours mix. The displacements of the projecting head are controlled by signals resulting from information recorded in a micro-processor.
One object of the present invention is to provide means for automatically mass-producing, at one time, high-resolution graphics composed of very small coloured dots which are very close to one another.
A further object of the invention is to provide an automatic machine or robot which comprises means for creating on a screen a graphic to be produced which may be polychrome and for automatically reproducing this graphic on a support which may or may not be flat.
Another object of the invention is to provide a machine capable of automatically reproducing, on various supports, an existing graphic, by enlarging it or reducing it or possibly modifying it, the colours being respected or modified.
Yet another object of the invention is to provide a robot for writing graphics which comprises means for automatically controlling correct execution of the graphics without being detrimental to the high-resolution qualities thereof.